1. Field of the Invention
The present invention relates to a front wheel suspension system for suspending a front wheel of a motorcycle, of the type wherein a link mechanism of the suspension system forms a quadrilateral on the side.
2. Description of Relevant Art
The conventional front wheel suspension system generally employed for motorcycles is of a telescopic type wherein a front fork for suspending a front wheel is formed of a retractable forked pipe and bottom cases.
A new type of suspension system is disclosed in U.S. Pat. No. 4,212,481 issued July 15, 1980. In such suspension system, a front fork is formed of an upper fork pivoted and held rotatably at the right and left sides of a vehicle body and a lower fork supporting a front wheel, and a link mechanism forming a quadrilateral on the side is provided on each side to connect both forks by two front and rear arms. When such link mechanism is deformed during operation, the front wheel will move up and down following the irregularities of the road surface and, when the two arms are diagonally downwardly converged to be non-parallel, the axle of the front wheel will be able to move up and down along a path substantially parallel with the axis of rotary operation of the handlebar and close to a straight line path. A shock absorber absorbing and cushioning the movement of the front wheel with the deformation of the link mechanism is provided on each side between two members of the two arms and lower forks, or between one member of the two arms and lower forks and the upper fork.
The advantages afforded by the aforesaid new type of suspension system wherein the link mechanism forms a quadrilateral on the side are that, due to the link mechanism, the front wheel moves more smoothly and the rigidity of the suspension system can be elevated so as to be higher than that of the telescopic type having sliding resistances between the forked pipe and bottom cases when extended and retracted. Further, the moving stroke of the front wheel can be enlarged to the extent that the property of the front wheel in following the irregularities of the road surface will be improved, and with the thus obtained large stroke, the extension and retraction of the shock absorber may be small and therefore the shock absorber can be made to be small and lightweight.
However, the aforesaid new type of suspension system also has a number of attendant disadvantages. Because two shock absorbers are provided, i.e., one for each of the two link mechanisms on the right and left sides, the weight of the suspension system is undesirably heavy. Further, the weight is so heavy that there is a problem in that the moment of inertia required to rotate the suspension system to the right and left by means of the handlebar is large. Because the shock absorber is mounted between the members forming the link mechanism, the position of the shock absorber is so close to the road surface as to cause a problem in that the shock absorber is likely to be adversely affected by mud or the like.
The present invention effectively eliminates the foregoing problems, while at the same time maintaining the advantages of a front wheel suspension system of the type wherein the link mechanism forms a quadrilateral on the side.